These pumps comprise two sets of rollers, radial and opposite with respect to the rotor supporting and rotating these sets of rollers. In each set of rollers, two rollers are linked and are separated from each other by a width such that the two walls of the tube are in contact and sufficiently compressed to ensure the tube's tightness during pumping.
Peristaltic pumps use an elastic elastomer tube that is relatively expensive, therefore it is important to ensure that this has a maximum useful life.
FIGS. 1 to 3 show such a peristaltic pump 1 according to the prior state of the art. This pump comprises a rotor 2 fixed on a drive shaft 3. Fixed on this rotor 2 are two symmetrically opposed sets 4, 5 of two rollers 6, 7 rotationally mobile around their longitudinal axis 8.
The two rollers 6, 7 of each set 4, 5 are positioned on either side of the tube 9 of the pump 1 and separated by a width e substantially equal to or less than the double width of walls 10, 11 of the tube 9, so as to ensure tightness in line with the compression of the tube 9.
When the sets 4, 5 of rollers move from the inlet 12 of the pump 1 towards its outlet 13, by the rotation of the rotor, the compressed portion of tube 9 reverts to its original cylindrical shape after the passage of these sets of rollers.
Through the movement, or rotation, of the sets 4, 5 of rollers, the product contained in the tube 9 is drawn in at the inlet 12 of pump 1 and ejected at the outlet 13. The continuous rotation of rotor 2 consequently ensures a pumped flow of the product drawn in at the inlet 12 and then ejected at the outlet 13.
The pumped flow is naturally proportional to the rotational speed of the rotor 2 and to the internal cross-section of the tube 9. The rotation of the drive shaft 3 of rotor 2 of pump 1 is carried out by a motor, not shown.
The rollers 6, 7 of each set 4, 5 are cylindrical and radial cylindrical rollers 14 and axial cylindrical rollers 15 fixed on the rotor 2 guide the tube 9 and keep it in a centered position on the rotor 2.
However, this pump 1 presents a number of drawbacks.
Firstly, it is noted that the axial cylindrical rollers 15 tend to embed themselves laterally at 16 in tube 9 under the latter's tension, since these rollers 15 only bear against one point. As a result, they deform the cylindricity of this tube 9 and reduce its suction capacity.
In addition, a cumbersome retention frame 17 is required to avoid having the tube 9 break away outwards.
In effect, it can be seen that, when these sets 4, 5 of rollers rotate, a traction force is applied on the part of the tube 9 located upstream of these sets 4, 5, which therefore tends to be elongated under this force, thus causing buckling of the part of the tube 9 located downstream of these sets 4, 5, which must therefore be held by this external frame 17.
In addition, the compression of the tube 9 by cylindrical rollers 6, 7 produces a variable linear speed V1 , V2 , V3 over their line of contact with the wall of tube 9, thus creating sliding between this latter and the rollers as a result causing wearing of the external wall of the tube and also heating of the latter that is harmful to the life of the tube 9.
Also, when the sets 4, 5 of cylindrical rollers arrive in front of the tube 9 to compress it during the rotation of the rotor, the sharp edge 18 located at the end of each roller 6, 7 strikes the external wall of the tube 9 and damages it, as a result also reducing the life of the tube 9.
Additionally, when the pump 1 is not utilized, it can remain stopped for a variable length of time, from a few hours to several months. The tube 9 therefore remains compressed by at least one of the two sets 4, 5 of rollers throughout the whole period during which pump 1 is not used. This can therefore lead to a permanent deformation of the elastomer of the tube 9, reducing the suction capacity of this tube 9 very substantially as a result.
It can even result in a decrease in the tube's suction capacity such that pump 1 is no longer able to pump and move any product.
Moreover, the force for compressing the tube 9 by the rollers 6, 7 spaced by width e must be the force required to ensure tightness during the pumping of the product at the maximum pressure that may be used. Because of this, the elastomer of the tube 9 is always subjected to a maximum deformation, not necessary when the pumping pressure is less.
Lastly, during the rotation of rotor 2, when one of the sets 4, 5 of rollers leaves contact with the tube 9 near the outlet 13 of pump 1, the two rollers 6, 7 are no longer driven by their friction on tube 9 and they therefore stop turning. Also when, after a certain rotation of rotor 2, these rollers 6, 7 arrive at the inlet 12 of pump 1, they come into contact with the external wall of tube 9 with a zero rotational speed and therefore abruptly start rotating. This results in damage to the external wall of tube 9 in line with the two impacts caused by the two rollers 6, 7, thus reducing the life of said tube 9.